Process for recovery of uranium and the upgrading of alkali-uranium fluoride precipitates



Unit d State P PROCESS FOR RECOVERY OF URANIUM AND j THE UPGRADING OF ALKALI-URANIUM FLU- PRECIPITATES V Richardll. Walnut Creek, Robert 0. Lindblom and 7 Claims. (Cl. 23-14.5)

'This invention relates to a process for increasing the uranium content and decreasing the content of other materials in certain alkali metal uranium fluoride precipitates In the operation of ion exchange processes for recovering uranium from various materials, there is produced a variety of eluates containing uranium and various impurities. Processes of this character are disclosed in the copending applications of Richard H. Bailes and Ray S. LongpSerial Numbers 155,307 and 165,532, filed April 11, 1950 and June 1,1950.

In said applications there aredisclosed processes wherein anionic 'exchangeresins are employed to absorb uranium in the uranyl state from industrial phosphoric acids or other crude phosphatic solutions. Subsequently, uranium is eluted by various methodswhereby there is produced a solution containing uranyl uranium and a complex mixture of other materials; Uranium eluate solutions, particularly dilute chloride eluate or acidic chloride eluate solutions, produced by the said processes are suitable for treatment by the present process.

Now it has been discovered that. the uranium values contained in such eluates can be recovered'by a'primary process wherein the uraniumis precipitated as impure tetravalent double fluoride compounds with alkalimetals including the compound NaUFs. Furthermore, the invention provides-a method whereby the uranium content of the precipitate can. be raised by 'a significant amount by treatment with dilute HF solution.

Accordingly, it is an object of the invention to provide a method for purifying and recovering uranium from certain impure solutions thereof.

A further'object'of the invention is to provide a method for purifying and recovering uranium contained in eluates obtained from an anionic exchange recovery process.

A still further object of the invention is to provide a method of purifying and recovering uranium from anionic exchange process eluates by treatment with fluoride and reduction to precipitate an alkali metal uranous fluoridefi a 7 Another object of the invention is to provide a process forupgrading the uranium content of an alkali metal uranous fluoride precipitate by treatment with HF.

Other objects and advantages of the invention will become apparent from consideration of the following specification. l I

In general, in operating anionic exchange uranium recoveryprocesses of the character noted above, uranium is adsorbed from an oxidized solution which also containsc'omplexingagents such as phosphate, chloride, sulfate,z'etc., on a strongly basic anionic exchange resin. Subsequently, the uranium is eluted with appropriate elutriantsolutions such as NaClor HCl-NaCl mixtures wher'ebythere is :obtainedan eluate solution containing uranium and a variety of impurities. For example, such an eluate may have a composition similar to that listed in the following table or may contain the impurities in ice much diflerent concentrations. These impurities may be lacking and other impuritiesmay be present, dependent upon the original solution composition, elutant composition and/or kind of materials added to theelutant,

TABLE I Constituent: Concentration, g./l. U308 0.29 F- 0.88 Si 0.10 Ti 0.07 Cl* 28.5 SO4= 9.2 P04 5 1.4 S02 3.5 V205 0.02 pH Ca 1.1

In accordance with the invention, a uranyl solution of the character described is treated with a solution of HP to provide an excess of fluoride ion therein. Subsequently, the pH of the solution is modified to a value within a quite definite range to provide a proper environment for the subsequent precipitation of the uranium. Then the solution is treated with a reducing agent such as electrolysis or a chemical reagent, preferably, Na2S2O4, to reduce the hexavalent uranium to the tetravalent state whereupon a sodium uranous fluoride precipitate is formed in the solution.

It is essential in carrying out the foregoing procedure to provide the following conditions: A slight excess of fluoride ion and considerable sodium ion (above about 1 M) must be present and the pH of the solution should be in the range of about 1.1 to about 5.0, with a value of 2.0 to 3.0 preferred. Only a slight excess of fluoride should be present as a large excess will fail to precipitate the uranium since soluble fluoride complexes appear to be formed with this excess fluoride condition. With insuflicient fluoride, various unsatisfactory precipitates such as uranous phosphates, etc., are formed and much uranium will remain in the solution. Reduction is carried to the point where all of the uranium is in the tetravalent state. Maximum precipitation is obtained at a temperature of 1020 C. The sodium uranous fluoride precipitation is advantageous since the material is easily filtered and is stable towards oxidation in air whereby uranium would be redissolved and lost in filtrates and washes. Other alkali metals, e. g., K, Li, etc., produce similar precipitates. When impurities are present which are capable of reacting with the fluorides, e, g., Si, Ti, etc., additional fluoride ion is supplied to compensate therefor. The composition of the precipitate will vary from fairly pure NaUFs when prepared in solutions containing few impurities to a highly contaminated mixture of uranous compounds including NaUFs and NazUFe When prepared from more highly contaminated solutions.

'It will be noted from the foregoing that the presence of sodium and additional fluoride in the compounds NaUFs and NazUFs, as well as the presence of various impurities, reduces the proportion of uranium in the precipitate. In accordance with the invention the proportion of uranium in the precipitate is materially increased in the following manner: The sodium uranous fluoride precipitate is separated as by filtration from the solution. Then the precipitate is washed with a dilute aqueous solution of HF whereby sodium and fluoride, at least, are removed from the precipitate yielding a material containing UF4 and, consequently, a much higher proportion of uranium.

With NaUFs the overall reaction which takes place :is believed to be as follows:

NaUFa-l-HF-eUFr-I-NaHFz It will-therefore be apparent that the compound NaUFa is of value in the production of uranium tetrafluoride. Following completion of the washing step the purified precipitate is readily dried' in air at about 110 C. Other. alkali metal uranous fluorides would behave similarly as should be apparent to those skilled inthe art.

Further details of the process of the invention will become apparent from the following examples.

Example I A. series of precipitation experiments were performed using actual and. synthetic anionic exchange eluates while maintaining the pH above about 1.5 since previous experiments indicated that sulfur was formed from the reducing agent. at. lower pH. values. Nosulfur formation wasnotedin these experiments. NazSzOqand 1 gram of HE per. gramof U308 were added-to the solution. The data for these precipitations are presented in Table II. Filtration of. the .product yielded a granular green precipitate which. is easy to filter. Drying yielded a slightly impure NaUFsproduct.

TABLE 11 PRECIPITATION-O11 URANIUM FROM 1 M NaCl ELUATES WITH Na2S204 AND HF 5'0 m'l. samples of either Head A or B used. 30 mg. of HF, representing 300% of the stoichiometric amount of fluoride necessary for complete conversion of uranium to NaUFs, was added. The pH was adjusted with NH;

or HCl. NazSzOr added as a freshlyprepared solution.

Head A (actual B (syntheteluate) ic soln.)

UsOa.-(g./l.) 0.58 0.56 S01 (g./l.) 16 16 C1- (g./l.) 0. 8 M 0. 8 M F- (g./l.) 0.87 Ti (g./l.) 0.15 0

NazSzO4 pH Fil- U 0 in Head added, before Treatment trate filtrate, Percent Soln mg. NaaSzOr pH g./l. Pptn.

addn.

15 2. 2 Stood. 4 hrs. at 3. 2 0.002 99.7

Rm. Temp. 25 2. 2 d 3.1 0.001 99.9 35 2. 2 2. 9 0.011 98. 1 45 2. 2 3. 2 0. 021 96. 4 1.0 2. 2 3. 9 0. 33 44 15 2. 2 3. 9 0. 16 73 20 2. 2 3. 9 0.04 93 25 2. 2 ..do 3. 9 0.007 98. 8 l 2. 2 NazSzol addn. 4.0 0.035 94 at 60 0. cooled 3 hrs. 25 2. 2 4. 2 O. 002 99. 8 35 2. 2 4.1 0. 003 99. 5 45 2. 2 3. 9 0. 002 99. 3 3O 1. 5 4. 5 0.002 99.8

Example II In. this. experiment there was employed an actual eluate (ca. 1 M.NaCl) having the following composition:

U308 g./'l 3.84 Cl g./ l 35 SO4=- 'g./l 6.0 V -g./-l 0.02 Fe; g./l 0.003 pH; 1.5

0.7 g. of HF and 0.8 g. of =Na2S2Ol per gram of U308 were added to the" eluateto:precipitate.theniranium. After filtration and drying the analysis of the product was as follows:

Example III A pilot plant uranium eluate of about pH 1.8' containing S02, Cl,.N-a+,. Si, F, and other minor impurities was treated with caustic. soda'to raise'the pH somewhat, HF was added, and then NazS2O4, to precipitate the uranium. The precipitate contained NaUFs and some NazSiFe with other minor impurities giving aproduct with the following typical analysis:

Substance U Na Si 13 Percent 42 I 3. Mole Ratio 0 Example IV Crude NaUFi similar to-that described in Example III was washed with 2 liters of coldHzO and then 500 ml. of a 1.92% solution of'I-IFthereby being converted into UF4. The reaction appears to be as follows:

The resultant product had the" following composition, therefore being fairly pure UH:

[ Percent Mole ratio While there has been described in the foregoing what may be considered to be preferred embodiments of the invention, various modifications may be made therein and it is intended to cover all such that come withinthe scope of the appended claims.

What is claimed-is:

1. A process for recovering uranium values from analCldlC uranyl anionic exchange elu'ate containing sodium ions comprising adding a slight excess of HF to the so lution, adjusting the pH of the solution to a value in the range of 1.1 to 5.0; treating the solution with a reducing agent to convert the uranyl ions to the uranous state, thereby producing' a sodium uranous fluoride precipitate, separating the precipitate from the solution, washing the precipitate with a dilute hydrofluoric acid solution, whereby the sodium uranous fluorides in themecipitate are converted to UF4, and separating the UF4 from the solution.

2. The process as otherwise defined in claim 1' but wherein said pH valueis in the range of about 2.0 to 3.0- and wherein said hydrofluoric acid washing solution isabout 2% HF.

3. The method. of converting N-aUFs into UF4 comprising contacting the insoluble NaUFs with 'adilute solution of hydrofluoric :acid, whereby insoluble UF4 is produced, and separating the solution from the insoluble. UF4.

4. The process as otherwise defined in claim 1 but wherein said reducing agent comprises electrolysis of the solution.

5. The. process as otherwise defined in claim 1 but wherein said reducingagent comprises N-azSzOr;

6. A process fiocr recovering uranium values firom an 7. The method of converting an alkali metal uranous acidic urany-l anionic exchange eluate containing at least fluoride into UF4 comprising contacting the insoluble about 1 M of alkali metal ions comprising adding a slight alkali metal u-ranous fluoride with a dilute solution of excess of HF to the solution, adjusting the pH of the hydrofluoric acid, whereby insoluble UF4 is produced, solution to a value in .the range of 1.1 to 5.0, treating 5 and separating the solution from the insoluble UF4. the solution with a reducing agent to oonvert the urarnyl ions to the uranous state, thereby producing an alkali References Clted the file of thls Patel]t metal precipitate therein, separating the precipitate airom Mellor: Comprehensive Treatise of Inorganic and the solution, washing the precipitate With a dilute hydro- Theoretical Chemistry, vol. 12, page 75 (1932). Pubfluoric acid solution, whereby'the alkali metal fluorides 10 lished by Longmans, Green&Oo., London. in the precipitate are converted to UF4, and separating the Kat-z et 211.: The Chemistry of Uranium, page 377-9 UF4 trom the solution. (1951). McGraw-Hill Book 00., New York. 

1. A PROCESS FOR RECOVERING URANIUM VALUES FROM A ACIDIC URANYL ANIONIC EXCHANGE ELUATE CONTAINING SODIUM IONS COMPRISING ADDING A SLIGHT EXCESS OF HF TO THE SOLUTION, ADJUSTING THE PH OF THE SOLUTION TO A VALUE IN THE RANGE OR 1.1 TO 5.0, TREATING THE SOLUTION WITH A REDUCING AGENT TO CONVERT THE URANYL IONS TO THE URANOUS STATE, THEREBY PRODUCING A SODIUM URANOUS FLUORIDE PRECIPITATE, SEPARATING THE PRECIPITATE FROM THE SOLUTION, WASHING THE PRECIPITATE WITH A DILUTE HYDROFLUORIC ACID SOLUTION, WHEREBY THE SODIUM URANOUS FLUORIDES IN THE PRECIPITATE ARE CONVERTED TO UF4 AND SEPARATING THE UF4 FROM THE SOLUTION. 